1. Field of the Invention
The present invention relates to a shift range switching apparatus, and particularly relates to an electronically-controlled shift range switching apparatus that switches the shift range of an automatic transmission by driving an actuator.
2. Description of the Related Art
In recent years, an electronically-controlled shift range switching apparatus that switches the shift range of an automatic transmission by driving an actuator including an electric motor has been practically used. In such a shift range switching apparatus, when a driver selects a desired range from the P (Parking), R (Reverse), N (Neutral) and D (Drive) ranges by operating a shift lever as a gear shifting instruction member, a shift range switching mechanism (a mechanism that slidably displaces in a mechanical manner a manual spool valve for switching between hydraulic circuits in the automatic transmission depending on the shift range selection by the driver) switches between actual shift ranges of the automatic transmission. For this apparatus, a shift-by-wire system is provided that is configured to convert the information on the shift range selection by the driver into an electric signal, then drive a motor using the converted electric signal to switch the shift range switching mechanism.
In the shift-by-wire system, a detent mechanism is placed between the motor and the shift range switching mechanism. When the motor is driven, a rotary shaft is caused to rotate, then a detent plate coupled to the rotary shaft to form the detent mechanism is caused to rotate. At this time, a detent spring is positioned at a notch that is an engagement part formed in the detent plate in connection with each range, which positions the detent plate, thereby positioning the shift range switching mechanism.
In this configuration, in order to detect the position of the shift range switching mechanism, the rotational position of the detent plate is detected by a detent position sensor, then, based on the deviation of the actual rotational position detected by the detent position sensor from a preset target rotational position, feedback control is performed by an actuator controller.
For example, in a method disclosed in JP-A-2002-357268 (Patent Document 1), after the actuator is driven based on the deviation of the actual rotational position from the target rotational position, the actuator is driven at full power until reaching a certain position, then the actuator becomes servo-controlled to be driven until reaching the target position, in which, on switching from full power drive to servo-controlled drive, the actuator is rapidly decelerated by reverse control, then the actuator is driven to converge on the target position under fine tune control.
Furthermore, in a method disclosed in JP-A-2003-148608 (Patent Document 2), when the motor control is switched is detected depending on the change in the load torque of the motor detected by a torque sensor, and the control signal depending on the deviation of the actual rotational position from the target rotational position is corrected depending on the load torque.
[Patent Document 1] JP-A-2002-357268
[Patent Document 2] JP-A-2003-148608
According to the method disclosed in the Patent Document 1, in order to perform deceleration control by reverse drive, it is absolutely necessary to include an inhibiting process or an overcurrent protective circuit for preventing current from flowing through the motor drive circuit when the drive direction of the motor is changed from forward to reverse. Furthermore, since the load torque non-linearly varies depending on the detect mechanism and also varies depending on a combination of shift patterns or an environmental change, enormous man-hours is needed for adapting a feedback control parameter or setting a feedback control gain according to an operating characteristic of the actuator, the amount of load or the like.
Furthermore, according to the method disclosed in the Patent Document 2, optimum control can be performed even when the load torque non-linearly varies due to the detent mechanism, but an additional torque sensor is required, which increases the cost.